Shelling broke a United Nations-brokered ceasefire in the government besieged Syrian city of Homs on Saturday as mortar rounds landed near an aid convoy as it tried to cross into the rebel-controlled old city district.

Syrian state television reported that four members of the Syrian Red Crescent were wounded in the attack, which it described as a terrorist attack and were trapped on the rebel side as night fell and the cease-fire expired.

Both sides accused the other of breaking the cease-fire. In a statement, the Red Crescent described the attack as deliberate but made no reference to who had conducted it. The Syrian Observatory for Human Rights, a Britain-based pro-opposition group that monitors violence in Syria, blamed government forces.

The difficulties in Homs came as the United Nations Relief and Works Agency announced that it had been told to stop its aid distribution program in the Yarmouk district of Damascus because of fighting.

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In a statement, UNRWA spokesman Christopher Gunness said the agency was pressing authorities to let it continue the program, which has delivered 6,300 food parcels since Jan. 30. Each parcel is designed to feed between five and eight people for 10 days. An estimated 18,000 civilians remain in Yarmouk, which began its existence as a Palestinian refugee camp, but became an urban neighborhood that once was home to 160,000 people, including Syrians.

“Clashes have taken place in the northern part of the Palestinian refugee camp in Damascus, Yarmouk, including in the area close to the distribution point where UNRWA has been handing out food parcels,” Gunness said. “Citing those clashes and the insecurity in the area, the authorities have advised that UNRWA’s food distribution should not continue until the area is secured.”

In its statement about the mortar attack in Homs, the Red Crescent said its trucks had just begun to enter the rebel-held Hamadiyeh neighborhood Saturday morning when mortar rounds landed near the convoy, which then came under small arms fire. At least one member of the team was wounded, the statement said.

Despite the shelling, most of the aid trucks arrived at their destinations, and the Syrian government hailed the delivery of supplies to the area.

Saturday’s events followed the successful evacuation Friday of 83 mostly elderly civilians from the old city district.

Homs, Syria’s third largest city, was one of the first areas to rise up against Syrian President Bashar Assad in 2011 and has been the scene of brutal fighting for much of the civil war. The central old city district has been under siege by pro-government forces since July 2012, and residents say most of the buildings have been destroyed and most of the civilian population has fled. An estimated 2,500 civilians are thought to still be in the district.

International officials who helped broker the deal said they hoped the arrangement would prove that similar arrangements could help relieve the humanitarian crisis in other areas. But rebel forces have expressed concern that the government would use cease-fires and aid delivery programs to consolidate gains and identify enemies in the civilian population.

On Saturday, the Syrian Opposition Coalition, the U.S.-backed opposition group that is expected to begin a new round of peace talks in Geneva with a Syrian government delegation, on Saturday warned in a statement that the Assad government “has used similar deals to buy time to strengthen its positions on the ground and to kill more civilians.”

Before announcing the pause of UNRWA’s Yarmouk program, Gunness reported in a separate email that UNRWA crews on Friday had witnessed a “steady stream” of people leaving the camp during the food distribution. He said Syrian authorities had said 77 people were evacuated from Yarmouk on Friday but that UNRWA could not vouch for the number because it was not “directly involved in this process.”